Effects of aging on Ca 2+ signaling in murine mesenteric arterial smooth muscle cells

Abstract

Pathophysiological changes in arterial smooth muscle structure and function occur with aging and there are a number of reports illustrating reductions in vascular responsiveness with aging. While much is known about arterial remodeling and functional adaptations with aging, very little is known about the biophysical adaptations in individual arterial myocytes. Cytosolic Ca 2+ signaling, involving activation of L-type Ca 2+ channels on the plasma membrane as well as InsP 3 and ryanodine receptors on the sarcoplasmic reticulum, is integral to vascular tone and reactivity. Thus, we tested the hypothesis that aging results in reductions in the functional expression of L-type channels and temporal aspects of ryanodine receptor and InsP 3 receptor Ca 2+ signaling, in mesenteric arterial smooth muscle cells isolated from 6 and 30 months old C57Bl/6 mice. Comparisons of L-type current activity were made using dialyzed, whole-cell voltage-clamp techniques and Ba 2+ as charge carrier. Ca 2+ signaling was measured using fura-2 fluorescence microscopy techniques. Cell morphological changes were also investigated using electrophysiological and immunocytochemical approaches. The amplitudes of L-type Ca 2+ currents were increased in older mice, but this was associated with membrane surface area increases of ∼50%, due to increases in cell length not cell width. Consequently, L-type Ca 2+ current densities were preserved with age, indicating functional channel expression was unchanged. In contrast, aging was associated with decrements in Ca 2+ signaling in response to either ryanodine receptor stimulation by caffeine or InsP 3 receptor activation with phenylephrine. These changes with aging may be related to the previously reported depression in myogenic reactivity.